This invention relates generally to semiconductor lasers, and, more particularly, to an optically pumped continuous wave semiconductor ring laser.
Lasers exist in many shapes and forms, yet search for new types of lasers continues unabated. Lasers vary greatly in many aspects such as, for example, power, operating wavelength, cavity design, method of pumping and mode discipline (mode-locking, single-frequency, or chaotic operation). The single, most frequent means of laser identification is by the type of gain medium utilized within the laser, since the medium will strongly influence, if not dictate, the other considerations of laser design.
Optically pumped semiconductor lasers are of especially great interest because of their potential for becoming a convenient, tunable, coherent source of electromagnetic radiation throughout the visible and near IR range of the spectrum. The most distinguishing feature of the semiconductor laser is that it does not deal with gain centers (atoms, ions, molecules, complexes) sparsely distributed in a passive medium or empty space, but rather with the phenomena of inverting the atoms in an entire block of solid material, unlike any other kind of laser. Excellent examples of an optically pumped semiconductor laser can be found in an article by C. B. Roxlo, D. Bebelaar, and M. M. Salour, "Tunable cw bulk semiconductor platelet laser," Applied Physics Letters, Vol. 38, No. 7, 1 Apr. 81, pp 507-509 and an article by C. B. Roxlo and M. M. Salour, "Synchronously pumped mode-locked CdS platelet laser," Applied Physics Letters, Vol. 38, No. 10, 15 May 81, pp 738-740. The optically pumped semiconductor laser combines the advantage of an increased spectral range over dye lasers with the possibility of intracavity tuning elements not available in diode lasers.
It has also been recognized that ring dye lasers are capable of producing substantial single-frequency output power as well as the shortest duration pulses thus far measurable when mode-locked. An excellent example of such a type of ring dye laser can be found in an article by S. M. Jarrett and J. F. Young, "High-efficiency single-frequency cw ring dye laser," Optical Letters, Vol 4, No. 6, June 1979, pgs 176-178. It would therefore appear to be extremely advantageous to combine the benefits provided by the ring laser with those of the optically pumped semiconductor laser. Unfortunately, the utilization of the solid, semiconductor lasing medium in place of the lasing medium found in conventional ring lasers has presented a number of problems heretofore insurmountable.
Generally, prior attempts at producing an optically pumped semiconductor ring laser have led to unacceptable results ranging from unreliable lasing to a complete destruction of the semiconductor lasing material. A major problem associated with such past attempts has been related to the fact that the use of a semiconductor lasing medium as typified in the optically pumped semiconductor laser of, for example, the type described in the above-mentioned articles in Applied Physics Letters by one of the present inventors does not obviously lead one to the conclusion that the semiconductor possesses the transparency necessary for ring laser operation. It was generally believed that the properties which allow the semiconductor to be used as a lasing medium in a conventional-type resonant cavity, adversely affect its use in the ring laser. Furthermore, even overcoming the above problem only leads to further problems. For example, the severe heating of the semiconductor lasing medium in a ring resonant cavity which would take place during laser operation can completely destroy the semiconductor itself.
If, however, an optically pumped semiconductor ring laser could be developed, it would appear to have all the advantages of prior semiconductor lasers and, in addition, provide increased power, and ease of operation.